Time-dependent density functional theory studies of the photoswitching of the two-photon absorption spectra in stilbene, metacyclophenadiene, and diarylethene chromophores

Photochromophores such as cis-stilbene (1a), metacyclophenadiene (2a), and the diarylethene 3a undergo photoinduced conrotatory opening and closing of a central bond and are currently being sought out as potential candidates for media within 3D optical information storage devices. Strong molecular two-photon absorption (inducing the reversible photoisomerization) is a necessary feature for this application due to the need for high 3D spatial resolution. Here, the one- and two-photon absorption (OPA and TPA) characteristics of the open- and closed-ring isomers of 1-3 have been investigated using time-dependent density functional theory. It was determined that the excited states populated by two-photon absorption were nearly 1 eV higher in energy than the lowest energy excited state populated by one-photon absorption. The electronic structures of the TPA and OPA accessed states were then compared utilizing natural transition orbital analysis. There, it was found that states excited by OPA had pipi* character about the C-C framework associated with the bond formation/scission of the central C-C bond. In contrast, the states populated by TPA have pipi* character along the C-C skeletal periphery, including phenyl excitations. It is postulated that these differences in excited state electronic structure may lead to reaction pathways alternative to photoisomerization about the central C-C bond, impacting the utility of these compounds as 3D information storage media.     

The sign and magnitude of 2hJ(F,F) and 1hJ(F,H) in FH...FH. A CLOPPA analysis of their distance dependence

The sign change of the intermolecular (2h)J(F,F) coupling in the (HF)2 dimer as a function of the F-F distance is discussed by means of the CLOPPA method. It is found that it is due to the competition of positive and negative contributions involving the interaction of the sigma lone pair of the acceptor nucleus with vacant molecular orbitals localized in the F-H...F moiety and with other molecular orbitals localized in the donor molecule. The origin of the sign of each contribution is fully determined by analyzing the response of the electronic system to the magnetic perturbation at the acceptor F nucleus. (2h)J(F,F) coupling in the FH...F-, which is positive for all F-F distances, is also analyzed in order to look for the differences with the former case.     

Refinement and use of the approximate similarity in QSAR models for benzodiazepine receptor ligands

Several considerations for refining the approximate similarity measurements have been introduced in this paper: the use of topological invariants for the calculation of similarity indexes and the development of new similarity correction processes. The quality of the new similarity measurements obtained with the proposed methods has permitted the development of fast, cheap, and simple quantitative structure-activity relationship models for the prediction of biological activities of nonbenzodiazepine gamma-aminobutyric acid(A)/benzodiazepine receptor ligands (58 compounds). Internal and external validations were carried out for the approximate similarity matrices computed using different approaches. Satisfactory results which compare reasonably well with a 3D approach were obtained: Q2= 0.65 and standard error in cross validation SECV= 0.83 for the training stage; r = 0.79 and error in external prediction = 0.82 for the test step. In addition, the method proposed was compared with other topological approaches based on constitutional similarity and on fingerprints. Satisfactory results were obtained.     

A suitable preparation of <Emphasis Type="Italic">N</Emphasis>-sulfonyl-1,2,3,4-tetrahydroisoquinolines and their ring homologs with a reusable Preyssler heteropolyacid as catalyst

The preparation of N-sulfonyl-1,2,3,4-tetrahydroisoquinolines, N-sulfonyl-2,3,4,5-tetrahydro-1H-2-benzazepines and N-sulfonyl-1,2,3,4,5,6-hexahydrobenzazocine was catalyzed by a Preyssler heteropolyacid, H₁₄[NaP₅W₃₀O₁₁₀], (PA), supported on silica (PASiO₂40) with excellent yields by means of the Pictet–Spengler reaction of N-aralkylsulfonamides with s-trioxane. The reactions proceed with 0.5 mol% of silica-supported catalyst in toluene at 70°C. The catalyst can be recycled without appreciable loss of the catalytic activity.     

Plasma- and vacuum-ultraviolet (VUV) photo-polymerisation of N- and O-rich thin films

Nitrogen (N)- and oxygen (O)-rich organic thin films were deposited by vacuum-ultraviolet (VUV)-assisted photo-chemical polymerisation of flowing ethylene (C₂H₄)–ammonia (NH₃) and C₂H₄–nitrous oxide (N₂O) mixtures of varying ratios, R, respectively. The reaction mechanism of these binary gas mixtures was investigated as a function of the wavelength, λ, of two near-mono-chromatic VUV sources. Surface-near compositions of these “UV-PE:N” and “UV-PE:O” films were determined by X-ray photoelectron (XPS), and by Fourier transform (reflection–absorption) infrared (FTIR) spectroscopies. The two types of films were compared with plasma polymers deposited using low-pressure radio-frequency (r.f.) glow discharges in similar gas flow mixtures, “PPE:N” and “PPE:O”. VUV-photochemistry appears to be superior to plasma-chemistry in its capability to produce nearly “mono-functional” organic thin films, ones that are rich in primary amines, –NH₂, and in carboxylic acid groups, –COOH, respectively.     

Annular tautomerism: experimental observations and quantum mechanics calculations

The use of MP2 level quantum mechanical (QM) calculations on isolated heteroaromatic ring systems for the prediction of the tautomeric propensities of whole molecules in a crystalline environment was examined. A Polarisable Continuum Model was used in the calculations to account for environment effects on the tautomeric relative stabilities. The calculated relative energies of tautomers were compared to relative abundances within the Cambridge Structural Database (CSD) and the Protein Data Bank (PDB). The work was focussed on 84 annular tautomeric forms of 34 common ring systems. Good agreement was found between the calculations and the experimental data even if the quantity of these data was limited in many cases. The QM results were compared to those produced by much faster semiempirical calculations. In a search for other sources of the useful experimental data, the relative numbers of known compounds in which prototropic positions were often substituted by heavy atoms were also analysed. A scheme which groups all annular tautomeric transformations into 10 classes was developed. The scheme was designed to encompass a comprehensive set of known and theoretically possible tautomeric ring systems generated as part of a previous study. General trends across analogous ring systems were detected as a result. The calculations and statistics collected on crystallographic data as well as the general trends observed should be useful for the better modelling of annular tautomerism in the applications such as computer-aided drug design, small molecule crystal structure prediction, the naming of compounds and the interpretation of protein—small molecule crystal structures.     

Mathematical modelling as a tool for the connection of school mathematics

We start introducing some aspects of the theoretical framework: the Anthropological Theory of Didactics (ATD). Then, we consider on the research domain commonly known as “modelling and applications” and briefly describe its evolution using the ATD as an analytical tool. We propose a reformulation of the modelling processes from the point of view of the ATD, which is useful to identify new educational phenomena and to propose and tackle new research problems. Finally, we focus on the problem of the connection of school mathematics. The reformulation of the modelling processes emerges as a didactic tool to tackle this research problem. We work on the problem of the articulation of the study of functional relationships in Secondary Education and present a teaching proposal designed to reduce the disconnection in the study of functional relationships in Spanish Secondary Education.     

Some effective heuristics for no-wait flowshops with setup times to minimize total completion time

In this work, we consider a complex flowshop scheduling problem in which both no-wait and separate setup times are considered. The optimisation criterion is the minimisation of the total completion time. We propose an effective dominance rule for the four machine case that can also be used for m machines. Five simple and fast heuristics are proposed along with two easy to code stochastic local search methods, one of them being based on Iterated Local Search (ILS). An extensive computational evaluation is carried out with two sets of 5,400 instances. All seven methods are compared to two recent algorithms. The results, confirmed by thorough statistical analyses, show that the proposed methods are more effective and efficient when compared to the best existing algorithms in the literature for the considered problem.     

Nullspaces and frames

In this paper we give new characterizations of Riesz and conditional Riesz frames in terms of the properties of the nullspace of their synthesis operators. On the other hand, we also study the oblique dual frames whose coefficients in the reconstruction formula minimize different weighted norms.     

Free radical synthesis of benzofused tricyclic β-lactams by intramolecular cyclization of 2-azetidinone-tethered haloarenes

o-Halogenophenyl- and o-halogenobenzyl-4-alkenyl-β-lactams can be prepared both in the racemic form and in optically pure form using the ketene-imine cyclization. These 2-azetidinone-tethered haloarenes were used for the regio- and stereoselective preparation of benzofused tricyclic β-lactams including benzocarbapenems and benzocarbacephems via intramolecular aryl radical cyclisation.